Carrier wave receiver



Feb. 18, 1936.

CARRIER WAVE RECEIVER Original Filed Dec. 21 1951 P. o. FARNHAM Re.19,857

Reisaued Feb. 18, 1936 mesne assignments, America, Delaware Re. 19,857UNITED STATES PATENT. OFFICE CARRIER WAVE RECEIVER Paul 0, Famham,Boonton, N. J., assignor, by

to Radio Corporation oi New York, N. Y., a corporation of Original No.1,910,099, dated May 23, 1933, Serial N0. 582,407, December 21, 1931.

Application for reissue July 17, 1934, Serial No. 735,715

6' Claims.

This invention relates to carrier wave receivers and more particularlyto receivers including a simple, eflicient and inexpensive automaticvolume control for rendering the rectified output substantiallyindependent of the strength of the received signals.

An object of the invention is to provide an improved carrier wavereceiver in which a single tube performs the function of a demodulator,a rectifier for supplying an automatic volume control voltage and anaudio frequency amplifier. A further object is to provide a carrier wavereceiver in which a multiple element tube constitutes a diode rectifierwhich delivers an audio frequency output to a local circuit and arectified carrier voltage to a gain control circuit, and an audiofrequency amplifier.

These and other objects of the invention will be apparent from thefollowing specification when taken with the accompanying drawing inwhich the single view is a fragmentary circuit diagram of a receiverembodying the invention.

In the drawing, the reference numeral l identifies a carrier waveamplifier which includes one or more tubes 2 which have input circuitsincluding inductances 3 tuned by condensers 4 which may be, andpreferably are, similar sections of a gang condenser. The low potentialterminals of the inductances 3 are grounded on their respective cathodesfor carrier frequencies by condensers v 5 and are connected to eachother and to an automatic gain control voltage line 6 that leads to thenovel detector stage that embodies the present invention.

The particular electrical design and the mechanical construction of thecarrier wave amplifier do not form a part of the invention. Theamplified signal voltage developed across the output terminals 1 of thecarrier wave amplifier l is impressed upon the tuned input circuit,comprising inductance 8 and tuning condenser 9,'of the multiple elementtube Ill. The tube Ill may be, as illustrated, a conventional screengrid tube having a cathode K, a control grid G1, screen grid G2 and aplate P, or it may include additional grid elements in accordance withknown tube practice. As will be apparent from the following description,the tube does not function as a conventional screen grid tube but as atube having a cathode, a control grid and two anodes.

The input circuit 8, 9 is not, however, connected between the cathode Kand control grid G1, but the high potential terminal of the inputcircuit is connected to the plate P and the lower potential terminal isconnected to cathode K through the resistor II that is by-passed, forcarrier frequencies, by a condenser I 2. With this circuit arrangement,rectification of a modulated carrier frequency voltage impressed on thetube from the tuned input circuit 8, 9 takes place by the diode actionbetween anode P and cathode K. The modulation component of the carriervoltage develops thereby an audio frequency component which is impressedon the control grid G1 for amplification. The average carrier leveldevelops a 5 direct current componentof voltage across resistor II whichis fed back to furnish automatic grid bias for the preceding amplifierstages.

The audio frequency voltage developed across the resistance II isimpressed upon the control 10 grid G1, by connecting the grid G1 to thepoint I3, i. e., the Junction of inductance 8 and resist ance 'I I. Thisconnection includes a condenser H to isolate the grid from the directcurrent com ponent of the rectified carrier voltage, and a filtercomprising a resistance l5 shunted to ground by condenser l6, whichfilter prevents any appreciable carrier frequency voltage from reachingthe control grid G1. A grid bias appropriate for audio frequencyamplification is impressed 50 on grid G1 from a source, indicated as C,through the bias resistor H. The primary winding of an audio frequencytransformer T is connected between the screen grid G: and a sourceofpositive potential +3, and the element G: therefore acts as the anodeof a triode amplifier having a cathode K and control grid G1.

The direct current component of the rectified carrier voltage developedacross resistor I I by the diode action of plate P and cathode K isimpressed upon the automatic gain control lead 6 by a connection l8extending from point l3 to lead 6 through the alternating current filternet work l9.

The following values are given as indicative of a design suitable foruse in the reception of carrier wave signals in the frequency band offrom 500 to 1500 kilocycles:

Resistance 11=200,000 ohms 40 Resistance 15=100,000 ohms Capacity 12:500micromicrofarads Capacity 14:5,000 mlcromicroiarads Capacity 16:100micromicrofarads Screen grid voltage, +B,=100 volts Control grid bias,C,=5 volts Inductance 8 and tuning condenser 9 were substantiallyidentical with the corresponding tuning elements 3, 4, respectively, ofthe carrier wave amplifier stages, and the transformer T was designed togive satisfactory audio fidelity characteristics.

As compared with the conventional use of a diode rectifier as ademodulator and a source of gain control voltage, the novel arrangementretains the advantage of the linear characteristics of the diodedetector and possesses the further advantage that the rectifier signalis amplified at audio frequency, thus increasing the sensitivity of thereceiver. Further advantages arise from 0thefactthatthecharacteristicsof theaudio amplifier are not ailected byvalue of the carrier input since the rectified carrier voltage isbypassed from control grid G; by the condenser l2. Astheprirnaryoftheaudiotransformer T isin the output circuit of an amplifier. and nota de-,

tector. the transformer may be of comparativeLv' inexpensiveconstructionas it is not necessary to employ a high impedance primary.

In the usual plate circuit rectifying detectors. the tube impedanceacross which the audio load is connected has been several times greaterthan in the case of the same type tube employed as an amplifier. Forfidelity over the audio frequency range. the audio load in the plate oroutput circuit should be constant over the audio range or, if notconstant, -should have values larger than the internal tube impedanceacross which it is connected. According to the present invention. thetube impedance across which the audio load is connected is relativelylow since the direct current potentials on the control grid and screengrid circuits are appropriate for amplification, not detection. Goodfidelity is v therefore obtained when the audio frequency transfu'merhas an impedance substantlalLv lower than that of the transformerswhich. when located in a detector output circuit, would give equallygood results.

I claim:

l. The combination with a carrier wave amplifier and a tube havingcathode, control grid, screen grid and plate elements, of circuitconnections for impressing between the cathode and plate elements theamplified carrier wave voltage developed by said amplifier, said circuitconnections including a resistor across which rectified direct currentand alternating current voltages are developed by the diode rectifieraction of said cathode and plate 'dements, means for impressing the saidalternating current voltage between the control grid and cathodeelements, and

means for returning to said amplifier a gain control voltage derivedfrom and proportional to the rectified carrier voltage developed acrosssaid resistor.

2. The combination with a carrier wave amplifier and a tube having acathode, first anode, control grid, and second anode; of circuitconnections for impressing between the'cathode and first anode elementsthe amplified carrier wave voltage developed by said amplifier, saidcircuit connections including a resistor across which rectified directcurrent and alternating current voltages are developed by the dioderectifier action of said cathode and first anode elements,

means for impressing the said alternating current voltage between thecontrol grid and cathode elements, and means for returning to saidamplifier a gain control voltage derived from and proportional to therectified carrier voltage developed across said resistor.

8. In a radio receiver, the combination with a radio amplifier; o a tubehaving a cathode, a rectifier anode, a control grid, and a positivelypolarized output anode; an input circuit for said tube uponvwhich. theradio output of said amplifier is impressed; said input circuit beingconnected between the cathode and the rectifier anode andincluding, inseries, a radio frequency coupling circuit, and a resistor shunted by aradio bypass condenser; means grounding the tube cathode for audio andradio frequencies, a couling capacity between control grid and the Junc-I tion of said resistor and radio frequency coupling circuit; an audiofrequency output circuit connected between the cathode and thepositively polarized output electrode; means impressing between saidcontrol grid and cathode a direct current bias potential eilective tosecure amplification in the audio frequency output circuit of audiofrequency variations impressed upon said control grid; and a directcurrent circuit for biasing said radio amplifier, said biasing circuitincluding the said resistor, whereby the gain of said radio amplifierisautomatically varied as a function of the radio input to saidreceiver.

4. In a carrier wave receiver, the combination with a carrier waveamplifier, of a tube having a cathode, control grid, screen grid andplate elements; an input circuit for said tube and upon which theamplified carrier wave output of said amplifier is impressed, said inputcircuit being connected between the plate and cathode elements of saidtube and including, in series, a tuned circuit and a resistor shunted bya carrier wave .by-pass condenser, means grounding the tube cathode foraudio and carrier frequencies, a capacity between control grid and thejunction of said resistor and tuned circuit, an audio frequency outputcircuit connected between the screen grid and cathode, and meansimpressing between said control grid and cathode a direct current biaspotential eflective to secure 3 amplification in the screen grid circuitof audio frequency variations impressed on said control grid, incombination with means including a direct current circuit connectedacross said resistor for automatically varying the gain of saidamplifier as a function of the rectified carrier voltage developedacross said resistor.

5. The combination with a radio amplifier and a tube having a cathodecooperating with a first anode to function as a rectifier and with acontrol grid and second anode to function as an emplifier, a diodenetwork including circuit connections for impressing between the cathodeand first anode the amplified radio voltage developed by said radioamplifier, said network including a resistor across which rectifieddirect current and audio frequency voltages are developed by the dioderectifier action of said cathode and first anode, means for impressingthe said audio frequency voltage between the cathode and control grid,and means including said resistor for impressing upon said radioamplifier a direct current biasing voltage which varies with the radioinput to said radio amplifier.

6. The combination with a high frequency sigi nal wave transmission tubeof an electron discharge tuhe provided with at least an electron emitterand an anode cooperating therewith to function as a wave rectifier, saidtube aditlitlonally being provided with a cold electrode and a secondanode to provide an amplifier, a diode network including circuitconnections for impressing between the emitter and first anode the wavestransmitted by said 11 tube, said network including a resistor acrosswhich rectified direct current and audio voltages are developed by thediode rectifier action, means for impressing the said audio voltage uponsaid cold electrode, and means including the resistor for im upon the ontube said direct current voltage as a gain control voltage which varieswith the wave amplitude.

PAUL O. FARNHAM.

